This invention relates to adhesive applicators, and, more particularly, to an applicator for dispensing hot melt adhesive onto a substrate such as the end flap structure of sift-proof cartons.
Hot melt thermoplastic adhesives are commonly used in applications such as packaging and cartoning where the quick setting time of this type of adhesive is advantageous. Hot melt adhesive applied to the flaps of a carton sets relatively quickly and substantially reduces the time in which compressive forces must be applied to the flaps while the adhesive bonds.
One type of cartoning application in which hot melt adhesives have proven effective is in bonding of the end flaps of sift-proof cartons. The hot melt adhesive pattern applied to the end flap structure of sift-proof cartons commonly includes a total of five discreet ribbons or strips of adhesive to effect a sift-proof seal. In order to provide a continuous line or bead of adhesive along the carton edge and prevent the formation of any minute channels or openings through which granular material in the carton could leak, the adhesive pattern must be accurately applied to the flap structure. This has been achieved in the prior art by mounting multiple adhesive guns above the path of the cartons and positioning the nozzles of the guns so that they contact the flap structures of the cartons. Direct contact between the nozzles of the adhesive guns and flaps ensures accurate placement of each of the five separate strips of adhesive.
One problem with this practice in the prior art is that of abrasion of the adhesive gun by the carton flaps. Nozzles are often fabricated of a relatively soft metal, such as cast aluminum or a similar lightweight metal, which has poor wear resistance. After a relatively short period of use, contact of such soft metal nozzles with the flaps results in abrasive wear which can distort the size and/or shape of the discharge orifice of the nozzle, and, in turn, the ribbon or strip of adhesive dispensed from the nozzle.
Another problem with prior art applicators for dispensing adhesives onto the flaps of sift-proof cartons, or other types of substrates, is that the vertical position of one adhesive gun relative to another is not readily adjustable to accommodate surfaces of different height. The desired vertical adjustment is not possible in some prior art adhesive applicators; in others it requires expensive modification of the gun.